1. Field of the Invention
The present invention relates to a composite type semiconductor such as a composite type diode in which the anodes or cathodes thereof are commonly connected.
2. Description of the Prior Art
The conventional center tap composite type diode is usually prepared by using diode pellet elements. For example, two diodes are soldered on one metal substrate.
In this case, it is necessary to find the polarity of the diode pellets before soldering the diode pellets on the substrate and it is necessary to provide sufficient space between the pellets so as to enable soldering of them during a soldering operation.
Accordingly, a problem with the conventional composite type diode is that a large space and a large metal substrate are disadvantageously required whereby a compact product cannot be prepared.
In order to overcome these disadvantages, a composite type diode having a plurality of diode elements on one semiconductor substrate has been developed.
FIG. 1 is a sectional view of one embodiment of the conventional composite type diode wherein two P type layers 12 and 13 are formed on the N type silicon single crystal substrate 14 to therefore form a pair of diode elements which are commonly connected to the cathode. However, when the conventional composite type diode is connected in the circuit of FIG. 2 to form a closed circuit which includes a DC power source 15, PN junction 16 at one end of the composite diode, a variable resistance 17 and (a) point 18 and a current I.sub.1 is passed through the closed circuit, a reverse current I.sub.2 is passed from the PN junction 16 to another PN junction 19 and the (a) point 18, certain undesirable effects occur. The value of the variable resistance 17 is changed to change the current I.sub.1 and the current I.sub.2 is measured. The relation of I.sub.1 and I.sub.2 is shown in FIG. 3, wherein the ordinate is the reverse current I.sub.2 passing through the junction 19 and the abscissa is the forward current I.sub.1 passing through the junction 18. When a forward voltage is applied to the junction 16 to pass the forward current I.sub.1, the reverse current I.sub.2 is changed in proportion to the forward current I.sub.1 and is passed through the junction 19 such as to result in interference between the diode having the P type layer 12 and the N type layer 14 and the diode having the P type layer 13 and the N type layer 14.
Accordingly, it is seen that the electrical characteristics obtained using the conventional composite type diode shown in FIG. 1 are undesirable and not practical in use.